Today, the use of fluorescence techniques such as fluorescence spectroscopy, fluorescence microscopy, flow cytometry or in vivo fluorescence imaging, allows the fast, clear, reliable and simple detection of the interaction between biomolecules, or the interaction of these biomolecules with other inorganic or organic molecules, such as drugs, for example. These techniques require the measurement of certain experimental parameters such as the excitation wavelength (λexc.), the emission wavelength (λem.), the intensity or quantum yield, the mean lifetime, and the fluorescence anisotropy.
A fluorescent probe suitable to be used as a nanosensor or bioprobe in drug discovery, genetic analysis, flow cytometry or high performance screening should have the following properties: it must be able to be excited without affecting the matrix it surrounds, easily detected, has a high quantum yield, is adaptable to the medium, for example, a cell culture, is stable and has functional groups which allow molecular labeling. It can also be favorable for these luminescent probes to have a long mean lifetime, to be non-toxic and that the luminescence parameters thereof are reproducible over time.
Today, the only fluorescent systems known having huge Stokes shifts of greater than 200 nm and slow decaying times of more than a microsecond are based on rare earth ions. However, they present multiple drawbacks such as: the difficulty in incorporating the same in matrices such that they do not lose their fluorescent characteristics; the existence of fixed and particular excitation, emission and Stokes shift characteristics corresponding to each rare earth, therefore they are not susceptible to being changed, and they are expensive and scarce materials. Examples of these systems are described in Sardar, D. K. et al., Biophotonics, January 2008; Resch-Genger, U., Advanced Fluorescence Reporters in Chemistry and Biology II Springer Series on Fluorescence, 2010, Volume 9, Part 1, 3-40; Harma H. et al., Analytical Chemistry, 2005, 77, 2643-2648; U.S. Pat. No. 7,465,747B2; US 2010/0224831 A1 and U.S. Pat. No. 4,283,382.
Therefore, it would be necessary to find luminescent probes that overcome these drawbacks of the nanoparticles based on rare earth elements.